Generalized hydraulic constitutive model of unsaturated flow in heterogeneous soils

This study develops a generalized constitutive model to describe hydraulic properties of soils that consider the soil heterogeneity and water distribution. In this model, pore size distribution in a cross-section of representative element volume is assumed as a fractal characteristic. The heterogeneity of soils is described by two heteroge-neous factors that calibrate the difference between local and bulk properties (i.e., porosity and water distribu-tion). Based on the capillarity, adsorptive mechanism, and laminar flow assumption, we derive a physics-based hydraulic model containing the water retention curve (WRC), relative water permeability (RWP) curve and relative air permeability (RAP) curve. Various data sets are employed to validate the proposed model and the results show that the RWP and RAP of unsaturated soils can be well predicted by parameters obtained from WRC data sets. Besides, in comparison with other models, the proposed model has a much better performance for most data sets. Finally, the influence of the dual-porosity characteristic of structured soils on hydraulic properties is also addressed.